Patent GB-1063037-A (GB)
Title: The measurement of magnetic fields
IPC: G11B5/39
Filed: 1964-05-11
Abstract: 1,063,037. Electric analogue calculating. SIEMENS' - SCHUCKERTWERKE A.G. May 11, 1964 [May 10, 1963], No. 19592/64. Heading G4G. [Also in Division G1] An arrangement including a magneto-resistive component for measuring a magnetic field comprises a coil, whereby in operation an alternating magnetic field can be applied to the component together with the field to be measured, a source of electric current for passing current through the component, and a filter circuit arranged so that it will pass only that component of the varying voltage drop which is attributable to the field. The arrangement may be used to obtain the. product of two or three variables by applying them to the arrangement as electric or magnetic signals. The; field may be concentrated in the vicinity of the component by mumetal rods. The element 1, Fig. 5, is subjected to the field to be measured and to a square wave alternating field from coil 5, and changes of component resistance as shown in Fig. 6c, are produced. Variations in the direct current from source 12 through the component are filtered by capacitor 13 and indicated on ammeter 14. In modifications described with reference to Figs. 7, 7a and 8 (not shown), the element is fed with the same A.C. as the coil and the meter which includes a series choke responds to the changes in virtual D.C. component arising from the field to be measured. In modifications of these later arrangements described with reference to Figs. 9; 10 (not shown), the coil and component are fed from separate secondaries of a transformer and the ammeter and choke are connected across the output diagonal of a bridge including the component and a balancing resistor which may also be magneto-resistive. Operation of the arrangement by sinusoidal A.C. is explained with reference to Figs. 12, 13 (not shown), and measurement by measuring the amplitude of a second harmonic created by a #/2 phase difference between the resistive changes, in the element and the applied A.C. is described with reference to Figs. 14 and 15 (not shown). An arrangement using two magneto-resistive components between the poles of two opposed U- shaped yokes in which the coils are connected to create alternating fields inphase opposition to produce a push-pull, effect is described with reference to Fig. 11 (not shown). In an arrangement. Fig. 16 (not shown), the magneto-resistive component (1) is mounted between the centre limbs of two E-shaped yokes (38), (39), the coils (40), (41) are wound around the centre limbs and the centre air gap is made small in relation to the outer air-gaps. The arrangement confines the alternating field so that disturbance of the field to be measured is minimized. A reading head for magnetic tapes, Fig. 17 (not shown), includes coils (40), (41), on yokes (44), (45), having a magneto-resistive element (1), and thetape is screened from the alternating field of the head by a screening foil of non-magnetic material of good conductivity. A modification of the reading head described with reference to Fig. 18 (not shown) includes two magneto-resistive components, one in each gap with the coil wound around the component. The head has two ferromagnetic members for conveying the field from the tape.